Was not test. Was OW encounters, every single one xebec we sunk. Several around Robras and Batabano, one of them was a 2v2 princes versus xebecs, both sunk. Again same spot a 2v2, one xebec sunk and other escaped. Others in Jamaica, bracketing with 7th and 6th rates while square riggers acted cheer leaders. Some others in Bahamas and US coast and Mosquito Coasts. Last one was in patrol zone with leaks and full HP, 8 leaks, and 30 seconds later was under.
They are not unbeatable but they are way more resilient than they should be.
Actually I think overall we killed more Xebecs than Hercules.